The invention relates to a wiper arm for a system for wiping windows, and more particularly for high-speed rail vehicles.
Numerous wiping arrangements have become known, particularly for motor vehicles. For example, European Patent Document EP-A-92201935.1 shows a wiping arrangement which comprises a wiper arm made of a composite material.
Nowadays, large-surface windshields are used not only in the automobile industry but also in rail vehicles, particularly in the high-speed operation, as, for example, in the case of the ICE (Intercity Railroad) of the Deutsche Bahn AG (German Railroad Corporation). Such windshields provide the required large and good field of vision for the driver of the traction vehicle.
Because of the high traveling speed, special problems occur in the operation with respect to wiping arrangements for wiping the front and rear windows of high-speed rail vehicles. Thus, the aerodynamic lift-off forces of conventional wiper arm bodies, for example, of the wiper arrangement according to European Patent Document EP-A-92201935.1, rise considerably at high traveling speeds, particularly above 120 km/h, so that the wiper blades of the wiper blade arrangement lift off the windshield during the ride.
In order to ensure a sufficient press-on force of the wiper blade, fastened to the wiper arm body and wiper arm, onto the windshield also at high speeds, wind deflector plates have been arranged on the arms and/or wiping blades of the arrangement known so far. The wind deflector plates counteract the lift-off forces which occur at higher vehicle speeds and reduce the press-on force onto the wiper blade.
However, it was a disadvantage of such deflector plates that they considerably restricted the field of vision of the traction vehicle driver and the effectiveness could not be ensured under all possible approach flow conditions. Furthermore, the solutions were very expensive and required high implementation cost because a large number of component parts had to be assembled to form a wiper arm arrangement.
It is therefore an object of the invention to provide a wiper arm for a wiper arm arrangement for wiping windows, particularly in the case of high-speed rail vehicles, to overcome the above-described problems of the state of the art.
In particular, a wiper arm is to be provided wherein the lift-off forces can be kept low also at high traveling speeds and simultaneously a field of vision for the traction vehicle driver is not reduced under unfavorable weather conditions. In addition, a solution is endeavored at reasonable cost.
According to the invention, these objects are achieved in that the wiper arm body of the wiper arm, over its whole length, has essentially a cross-sectional shape with a first curvature facing the windshield and a second curvature facing away from the windshield. The second curvature is smaller than the first curvature.
In such an embodiment of the wiper arm body, the overspeeds and therefore the vacuums occurring on the side of the wiper arm body facing the windshield cause a press-on force which increases with the traveling speed and which counteracts the aerodynamic negative lift forces. As generally in aerodynamics, a curvature in the present patent application is the characteristic of a cross-section which is the result of a curving, thus, of the deviation from a straight line from the nose to the end edge which represents the connection of the center points of circles placed in this cross-section and touching its outer contour.
In an advantageous embodiment of the invention, the curvatures are constructed such that the press on force, on the wiper blade fastened to the wiper arm body, in the whole traveling speed range of the high-speed vehicle up to speeds of 400 km/h, exceeds the aerodynamic lift-off forces of the wiper arm from the windshield. At both ends of a motor car or of a railway engine, the effectiveness of the present invention is independent of the alignment with respect to the traveling direction.
It is particularly advantageous for the curvatures to be selected such that the press-on force, on the wiper blades arranged on the wiper arm which occurs at different traveling speeds, assumes an essentially constant value.
In a first embodiment of the invention, the wiper arm body is a solid body.
As an alternative, the wiper arm body may also be designed as a hollow body. This advantageously permits the arrangement of lines inside the hollow body. An example are the supply lines for the spraying water supply.
The wiper arm body according to the invention expediently consists of a fiber composite, which permits the saving of a considerable amount of weight.
In order to ensure a sufficient flexural strength and resistance to bending in the case of wiper arm bodies made of such fiber composites, it is advantageous for the wiper arm body to have fibers which extend in the longitudinal direction as well as diagonally oriented fibers which provide a sufficient shearing strength and resistance to shearing.
Carbon fiber composites are used as particularly advantageous composites for the wiper arm body according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.